In image-forming apparatus such as copiers, printers, and facsimiles, electrophotographic systems in which charging, exposure, development, transfer, etc., are carried out using electrophotographic photoreceptors have been widely employed. In such image-forming apparatus, there are ever-increasing demands for speeding up of image-formation processes, improvement in image quality, miniaturization and prolonged life of the apparatus, reduction in production cost and running cost, etc.
A multi-layered photoreceptor employed in electrophotographic imaging systems sometimes includes one or more of a substrate, an undercoating layer, an intermediate layer, an optional hole- or charge-blocking layer, a charge-generating layer over an undercoating layer and/or a blocking layer, and a charge-transport layer. Additional layers such as one or more overcoat layer or layers are also sometimes included.
In the charge transport layer and the optional protective overcoat layer, hole transport molecules may be dispersed in a polymer binder. The hole transport molecules provide hole or electron transport properties, while the electrically inactive polymer binder provides mechanical properties.
Arylamine compounds can be useful as hole transport compounds in electrostatographic imaging devices and processes.
Production of arylamine hole transport compounds require the synthesis of intermediate materials, some of which generally are costly and/or time-consuming to produce, and some of which require a multi-step process.
For example, diarylamines may be produced using traditional Goldberg reactions. This method requires the derivatization of an aniline with acetic anhydride to produce an acetanilide compound. The acetanilide compound is then reacted with an arylbromide compound to produce an intermediate that must then be hydrolyzed in alcohol solution to produce the diarylamine compound. The formation of diphenylamines using the Goldberg reaction takes three reaction steps, and thus can be a lengthy process. Total cycle time for this process can be 3 to 5 days in the lab.
Diarylamines may be reacted with halogenated aryl compounds to form a variety of triarylamine compounds. See, e.g., U.S. patent application Ser. No. 10/992,690 filed Nov. 22, 2004.
Diarylamines may also be produced by subjecting an arylamine to condensation reaction in the co-presence of anhydrous aluminum chloride and anhydrous calcium chloride, as described in U.S. Pat. No. 6,218,576 B1 to Shintou et al. Both of these methods require high temperatures and harsh reaction conditions. The purity of the diarylamines obtained from these two reactions are generally low, requiring lengthy and costly purification processes.
As an alternative to the above methods, Buchwald chemistry may be important to produce arylamine compounds. The formation of di- and tri-arylamine compounds using Buchwald chemistry comprises reacting an arylamine with an aryl halide in the presence of a ligated palladium catalyst and base. This process has distinct advantages in regard to cycle time, energy consumption, and crude product purity over traditional methods.
Microreactors have been defined as “Microsystems fabricated, at least partially, by methods of microtechnology and precision engineering. Fluid channels range from 1 um (nanoreactors) to 1 mm (minireactors).” See Microreactors, Ehrfeld, Hessel & Lowe 2000, the entire disclosure of which is incorporated herein by reference. Typical microreactors consist of miniaturized channels, often imbedded in a flat surface referred to as the “chip.” These flat surfaces can be glass plates or plates of metals such as stainless steel or Hastelloy. Microreactors have proven to be highly valuable tools in organic chemistry due to their wide flexibility of operating conditions with efficient heat transfer, optimized mixing, and high reaction control. Advantages of a microreactor over more conventional batch reactions include: faster efficient mixing, selectivity enhanced-side products and secondary reactions reduced, higher yield impurity, extreme reaction conditions, time and cost savings, and increased surface area to volume ratio that results in good mass and heat transfer. Microreactors are particularly useful for rapid optimization, screening different reaction conditions, catalysts, ligands, bases, and solvents; mechanistic studies; cost effective industrial scale up; and rapid screening for new pharmaceuticals.
Although microreactors have distinct advantages over conventional batch reaction techniques, microreactor chemistry also has its own shortcomings. For example, microreactors generally do not tolerate particulate matter well, often clogging. Since the production of arylamines through Buchwald chemistry is highly exothermic during batch production, it is ideally suited for a microreactor. However, the Buchwald synthesis of arylamines is known to produce a precipitate of solid halogen salt, such as sodium bromide, as a byproduct. Therefore, there is a need for an improved method for the preparation of arylamine compounds using a microreactor.